How can you get free power? Well, one way is to steal it from other people. And if you steal it in small enough bites from a lot of people, they may never notice.

This seems to be the basic idea in this article in the Guardian, whose author clearly attended lots of journalism classes while studiously avoiding any class that might have made mention of the first law of thermodynamics.

"Green" speed bumps that will generate electricity as cars drive over them are to be introduced on Britain's roads. The hi-tech "sleeping policemen" will power street lights, traffic lights and road signs in a pilot scheme in London that could be rolled out nationwide.

Speed bumps have long been the bane of motorists' lives, but these will capture the kinetic energy of vehicles.

Peter Hughes, the designer behind the idea, said: "They are speed bumps, but they are not like conventional speed bumps. They don't damage your car or waste petrol when you drive over them - and they have the added advantage that they produce energy free of charge." An engineer who formerly advised the United Nations on renewable energy sources, Hughes added: "If it [the energy] wasn't harnessed by the speed bumps, it would go to waste."

The ramps - which cost between £20,000 and £55,000, depending on size - consist of a series of panels set in a pad virtually flush to the road. As the traffic passes over it, the panels go up and down, setting a cog in motion under the road. This then turns a motor, which produces mechanical energy. A steady stream of traffic passing over the bump can generate 10-36kW of power.

OK, I am willing to believe that you might be able to recover some net energy from a system with this kind of dynamic speed bump replacing an existing static bump (but I am skeptical, and would want to see the math). Of course, if you really have a road with a speed bump and so much traffic that it will generate this much power and repay a large investment, then you probably have a road/traffic design issue.

But the article seems to be positing that towns could install these as flat devices --"virtually flush to the road" -- that drivers would hardly notice. Power from these devices would help the town power its lights and other devices. But unless these guys have invented the perpetual motion machine, there is no free energy to be had here. In fact, due to that nasty old spoil-sport, the second law of thermodynamics, there has to be a total system loss. The device might only steal the equivalent energy of a thousandth of a gallon of gas from each driver, so the driver of each car won't really notice, but the total system expenditure of the thousands of drivers who power the device will still be there, just hidden. This is a new stealth tax on drivers, dressed up in green clothing.

Next up: Britain proposes to put windmills on the roofs of electric cars as a power source. After all, when you are driving at 60 miles per hour, all that wind energy coming past your car is just lost, right? Once you got the car up to speed, it would just generate its own electricity. LOL. I shouldn't laugh, there is probably a billion or so for this in Obama's stimulus bill.

You're right, though, the energy from the speed bumps isn't free. I'd love to see the thermodynamic efficiency calculation, including the part about where the energy gets generated in the first place... Just how much power would each set of wheels generate as it passed over the energy-recovery-bump. And just how much fuel would the car have to burn to produce that little bit of power? And if you do the math and convert it to gallons of gasoline per KW-Hr, I'll bet it's pretty inefficient. I'll bet a portable gasoline-powered electric generator is more efficient.

This would be a good idea if you put it in front of a stop sign... and if it cost almost nothing. 20k pounds minimum? Are you kidding me?

Fred from Canuckistan . . .

It never ceases to amaze me that the members of the Global Church of Climate Scientology can put logic on hold and who can embrace cognitive dissonance in such a rapturous manner.

When it comes to saving us all from our self inflicted global warming catastrophe, it seems the Laws of Physics need not apply, let alone basic common sense.

They just have to Believe.

CTD

Jamie,

That was unspeakably depressing. The amount of ignorance of even the most basic scientific principles (figured out, what, 350 years ago?) displayed in that article (by the subjects and the reporter) are jaw-dropping.

Douglas2

It might be bad reporting. The energy is "free" in that the local council is not paying by the kW/H. It might be considered "free" in terms of eliminating the need to trench in direct-burial cable between the place where the power is used and the place where the utility will provide it.
In the UK, the most common form of traffic control at intersections is the roundabout, and even extremely rural roundabouts have illuminated bollards to mark them and illuminated signs. If the traffic on the road was adequate to generate enough power to support the illumination, then it saves lots of upfront costs and is payed for by the actual users of the road.
Of course, having the trial in London pretty much negates the advantages above, but you do get to use the grid as your battery.
If they cost and work as expected the payoff time for the local councils is 1 to 10 years.
Think of it as distributed generation that will help take load off of the National Grid, will be sited congruent with population and power needs, and that it will be a road-pricing scheme that doesn't slow you down or compromise privacy.

Highway

One way I can see this fulfilling both a traffic calming and some energy recovery would perhaps be a combination of the generation aspect shown in Coyote's article with this kind of speed bump:

I agree that there's a parasitic drain from people using the roadway. However, it may be worthwhile to compare the energy and cost from this kind of scheme to the cost of providing the equivalent electricity and infrastructure to the signs through the existing power grid.

It's not like the electricity is free the old way, either.

Noumenon

At first I was with the people who said "it'll just help you brake at the stop sign," but if you think about it only the first two cars in line will go over it while braking. The rest will be accelerating. Coyote wins.

http://www.huntjohnsendesigns.com/ Hunt Johnsen

Hughes added: â€œIf it [the energy] wasnâ€™t harnessed by the speed bumps, it would go to waste.â€

Just a little handwave and the first law goes away! This green science is wonderful stuff eh Douglas?

http://neubranderinc.com/blog Nobrainer

Just to quibble with Noumenon, the 3rd car in line at a stop shouldn't be accelerating through the stop sign unless the driver is so bad that they believe stopping 10 yards before the sign counts as stopping at the sign.

But Noumenon is on the right track. If the system is installed at the wrong place then any perceived benefits, at least with respect to the entire system, are likely to be illusory.

On a side note, at least the numbers presented here seem reasonable. A couple years ago I ran across some Greek guys hawking their "kinergypower" system. Their system is probably similar, but they made the mistake of claiming benefits about 2 full orders of magnitude greater than physically possible while also claiming their product was "the solution to our energy crisis."

ErikTheRed

"In this house, we obey the laws of thermodynamics!"
-- Homer Simpson

Even idiot cartoon characters are brighter than that bunch.

Zach

Last summer, while trying to diagnose an air conditioner problem, I stumbled across a young lady asking in Yahoo Answers asking if she could cool her apartment temporarily by leaving her freezer door open. This prompted a rant on my blog about how stupid it was that I was forced to learn Shakespeare, Sophocles and a bunch of other junk in school that has yet to be useful to me anywhere outside of Trivial Pursuit, but this bimbo wasn't forced to learn the fundamental rules of the universe. A parallel rant was that her vote counts as much as mine does.

bbartlog

A steady stream of traffic passing over the bump can generate 10-36kW of power.

This seems implausible. Assume our stream of cars is going 100kph, spaced out one car every ten meters. This is 10,000 cars per hour; let's call it 3 cars per second. If each car pushes down a piston a distance of 10cm with a force of 1000n, twice (once for each set of wheels), that's 3 x 2 x 1000 x 0.1 = 600 Joules per second, or about 150 watts. And I believe the jolts would be quite noticeable with these parameters (though it could depend on the mass of the moving components). Then again, since this is a 'series of panels' maybe they are going to have a hundred of these things in a row...

As a thought experiment, we can figure out how much of a decelerative shock a perfectly efficient fixed-point 'momentum extractor' would have to inflict on passing cars in order to generate 30 kilowatts of power. Again, let's assume 3 cars per second, this time 25m/sec velocity, each car weighing 1000 kilos. Each car is packing 312,000 joules of energy (e=1/2mv^2), and we need to get about 120,000 joules per second (actually a bit more, I am using 1w = 4J instead of 4.18...), or 40,000 joules of energy from each passing car. So if we can reduce the velocity to 23.3m/sec and use that energy with 100% efficiency, we have our 30kW.
Assuming the car travels 4m in the 'deceleration zone', it will spend 1/6 of a second decelerating. 1.7m/sec / 1/6 = 10.2m per second squared, a little more than one g of deceleration.

Anyway, the only way this thing would be a free lunch is if you put it in some spot where people had to decelerate anyway, and preferably one where people are going kind of fast (stop sign is a lousy idea not least because you don't have high enough velocities at work). For example, on the downslope of a big hill. I'm sure it's still 100x easier to build a working wind turbine than this cockamamie thing, but it's not a total violation of thermodynamics.

JC

The trick will be to install such systems in households with small children, harnessing the seemingly inexhaustable energy therein released

David W

A slight quibble with bbartlog - the 4.184 factor is Joules/calorie - a Watt is still just a Joule/sec.

It's still going to be quite the bump, though, with half the speed loss.

JD

From the company site:

"Q1. Doesnâ€™t the ramp just steal pennies from our petrol tanks?
A1. The ramp is designed to be situated in parts of the roadway where vehicles are having to slow down, for example on downhill gradients, when approaching traffic lights or roundabouts as well as replacing sleeping policemen and traditional traffic calming measures.
In the these situations, the kinetic energy of the car is being dissipated into heat (i.e. through the braking system) anyway; the ramp at this point scavenges a degree of kinetic energy as the car passes over it, but this is far less than is lost through other mechanisms."

***

These could certainly be installed on highway off-ramps and downhill slopes where one must slow down anyway. Thus, some energy is captured instead of it being lost to heat/braking anyway. Speed bump replacement (as the article stated) is another viable use.

They are NOT proposing they be placed in the middle of normal roads but in places where one is braking and losing that energy to heat friction anyhow. It is all about placement. Effective placement is certainly beneficial and NOT being stolen from drivers.

markm

bbartlog: What David said, plus 1000 kg is the mass. The weight is the mass times the acceleration of gravity = 9800 newton. And, is 1000kg supposed to represent the weight on one axle or of the whole car? 1000kg (2206 lb) is an impractically light car for American collision standards, but maybe could be a small Brit car. 2000kg (4412 lb) is more like a small SUV and I assume would be far above the average Brit vehicle. Anyhow, to maintain comparability with bb's work, I'll assume a 1000kg car (balancing that against the 100% efficiency assumption), or 4900n on each axle, and round that up to 5000n. 10cm (4 inch) deflection sounds like a reasonable maximum.

We're only short of the claim by a factor of 10. I guess that's close enough for an engineer who worked for the UN, although my boss would fire me so fast...

What is the effect on the car? Say it's going 25kph (15mph), which is pretty fast across speed bumps. The KE is 1/2 (1000kg)(25000/3600 m/s)^2 = 24,000 J. Take away 1,000J and the new speed is 6.80 m/s = 24.5 kph. Not much of a jolt, but there will also be an up-and-down jolt. That vertical jolt is inefficient energy transfer, so I think if the device is built at all right, it won't jolt the car up and down nearly as much as a mild 2 inch speed bump, so there's a net improvement in the ride. (Or reduction in speed bump effectiveness, depending on your POV.)

It seems pretty obvious that they're never going to recoup the energy used to make these things and plant them in the roads. But perhaps it's a reasonable alternative to running power lines or mounting solar cells. So, is it believable that you could power a stoplight from this? I don't know about stoplights, but we're manufacturing LED streetlights that use 150W. Each car going by gives one light about 6 seconds of power. What happens if it's minutes between cars at 2 am? Better have big batteries, and better only do this at busy intersections so there's enough daytime traffic to charge them - but busy intersections are also where there's the most need to have a power backup, which in this case is probably a power line...

OTOH, I can see it working to light LED lane markers in a roundabout.

Alex

"which cost between Â£20,000 and Â£55,000"

Holy mother of... Are they retarded? ~$100,000 for a friggin' speed bumb? Even if it does generate a few thousand watts, a lot of it is just stolen from the drivers, it's still a tremendous waste of money.

For $100,000 you could provide solar panels for 10-15 few houses (or better yet, you could pool the money and build nuclear reactors).

Cha

"It's essentially free"

He meant, essentially free jobs for life for marginally talented engineers who have a phobia for working in private industry where you actually have to make real profits by serving people if you're going to survive.

"This guy is an engineer who used to advise the UN?"

Er, yes, I understand that before becoming an engineer he was a special diplomatic advisor to the U.N. on "how to avoid genocide in Rwanda", "how to establish good government in Haiti", and "how to avoid corruption in the Iraqi oil-for-food program".

http://deanesmay.com TallDave

"But unless these guys have invented the perpetual motion machine, there is no free energy to be had here."

Well, it's not technically free, but it is currently being thrown away via friction to the brakes.

This is actually a pretty good idea for places like exit ramps, where all that momentum that normally just goes into deforming your brake pads could be used to generate power. The only question is whether the "free" energy can pay for the cost of the apparatus.

http://www.xrdarabia.org John Burgess

All the scoffing is amusing as examples of knee-jerk "I'm smarter than you"-ism.

The fact is that the UK abounds in speed bumps ("sleeping policemen") as "traffic calming measures", as Douglas2 points out. You find them on most suburban streets. Other methods of forcing cars to slow are used in more urban areas. It remains a fact, however, that cars go over the bumps and lose kinetic energy. Some of that energy shows up in the cars' shocks and springs or as heat on the bump. The rest of the kinetic energy, as well as the potential energy represented by the pull of gravity on the car, is what's a question. This's pure physics and fully in compliance with the 2nd Law of Thermodynamics.

The proposal is to intended to harness the energy that would otherwise be lost (as Douglas2 also points out) by converting the up/down mechanical energy into electrical energy. No violation of laws here. It is 'leeching' or 'vampirism' only to the extent that new speed bumps would be built in order to generate power. Otherwise, it's just capturing energy that would otherwise be discarded.

Perhaps the process is not efficient. It might not be cost effective in the end. But since the energy lost from the cars passing over speed bumps is already drained from the cars momentum, it is not irrational to find a way to scavenge that energy and use it. Any tool or toy that works by converting a hand squeeze into rotary motion (like some pinwheels) can also be jiggered to convert it to electricity (as, for example, the newer battery-less radios). Doing it at a larger scale--i.e., vehicles passing over a pressure plate--certainly will work. Just how well it will work is the only question.